1. Field of the Invention
The present invention is directed to a method for positioning a catheter that has been inserted into a vessel and to a device for implementing the method, the device being particularly for conducting an angiographic examination of a subject.
2. Description of the Prior Art
In angiographic examinations, i.e. in radiological examinations of blood vessels or lymphatic vessels, a catheter is inserted into the examined vessel, by means of which a specific contrast agent can be injected into the vessel in order to improve the contrast of the captured X-ray image at the examined location, the corresponding vessel being brought into prominence in the X-ray image by the contrast agent injection. For this purpose the catheter must first be led to the respective target location, i.e. to the desired examination location. The positioning of the catheter in angiographic examinations thus has a special significance, since what is particularly important in the positioning of the catheter to follow the branchings of the vessel accurately and to reach the desired target location (where there is a stenosis or an aneurism [sic], for example) precisely and without interruption.
For this reason, a technique known as the road map technique (pathfinder technique) has long been used, which facilitates positioning of the catheter in a vessel that is to be examined. In this technique, a small amount of contrast agent is injected into the vessel via the catheter while transirradiating the vessel, and, as soon as the vessel gives an image, the transirradiation is interrupted and the last radiographic image is stored as a mask. After the transirradiation has been restarted, individual images are captured of the catheter inserted in the vessel that is to be examined, and these are superimposed on and subtracted from the stored mask image, so that an examiner can visually localize and place the catheter in the contrasted image by observing the superimposed total image.
The above-described road map technique requires that the instantaneous images of the catheter in the vessel be captured from the same exposure angle or projection angle of the X-ray device as the previously stored mask image, since otherwise these images can not be compared to the stored mask images, by being superimposed on them. As a result, in order to mark the individual vessels, it is necessary to make new contrast agent injections for each projection direction or for each exposure angle, so that difficult interventional procedures, such as those employed in the field of neuroradiology must be used. Since these procedures entail relatively frequent contrast agent injections, this makes rapid positioning and localizing of the catheter in the vessel to be examined difficult and prolongs the treatment period for the examination subject.
An object of the present invention is to provide a method for positioning a catheter which has been inserted into a vessel, as well as a corresponding device, which make it possible to position the catheter more rapidly and simply in the vessel which is to be examined and to avoid frequent contrast agent injections, in particular.
The basic idea of the aforementioned road map technique is also relied upon in the present invention for positioning the catheter in a vessel to be examined; that is, after a contrast agent has been injected, a contrast agent image is captured and stored as a mask of the respective vessel, the mask being superimposed by a subsequently captured single image of the vessel with inserted catheter, in order to be able to localize and place the catheter in the contrasted vessel using the thus-acquired total image. This is augmented in the present invention to achieve the above object by generating and storing a three-dimensional image of the vessel as the mask, this three-dimensional image being computed from a number of individual images that have been picked up from various projection angles or exposure angles with an X-ray device, by transirradiating the contrasted vessel. This procedure-makes it possible to select that individual image of the three-dimensional mask image whose projection direction, or whose exposure angle, most optimally corresponds to the instantaneous exposure angle of the instantaneous image, depending on the projection direction of the subsequent instantaneous exposure of the examined vessel. This selected individual image is subsequently displayed with the individual instantaneous images superimposed thereon, in order to be able to localize and place the catheter visually in the contrasted vessel.
Using the invention, only a one-time contrast agent injection is required in order to generate a three-dimensional mask image. The individual images, which, when reconstructed, yield the three-dimensional mask image of the contrasted vessel, can be captured by rotating the pickup system of the X-ray device around the examination location. The invention thus guarantees that, despite a single one-time contrast agent injection, it is always possible to select the appropriate mask image and to superimpose the instantaneous images thereon, regardless of the actual projection direction used to capture the instantaneous images of the vessel to be examined, so that new injections of contrast agent are not required for each new positioning direction. Using the present invention, it is thus possible to rapidly and precisely localize and position the catheter in the vessel, so that the catheter can likewise be guided in the vessel rapidly and precisely to the desired target location, (the location of the examination).
The present invention also makes it possible, subsequent to capturing the three-dimensional mask image of the vessel, to select the projection direction or the exposure angle for capturing the instantaneous images which is optimal for catheter guidance, and to adjust the X-ray device accordingly. For this purpose, it is merely necessary to select the individual image of the three-dimensional mask image that corresponds to the projection direction that has been set, in order to be able to subsequently superimpose the instantaneous images thereon.
The present invention can be used either in a monoplanar transirradiation or in a biplanar transirradiation of the examination location, the instantaneous images being captured from only one projection direction or from two different projection directions, respectively. It can be guaranteed by appropriate matchings that the selected mask image is always displayed congruently to the captured instantaneous image, by employing the known pixel shifting technique for this purpose.